1. Field of the Invention
The present application relates to a structure of separation of a photoelectric conversion apparatus.
2. Description of the Related Art
CCD type and CMOS type photoelectric conversion apparatuses are used for many digital cameras and digital camcorders. In recent years, in the photoelectric conversion apparatuses, pixels have been reduced. Accordingly, measures against mixing of charges to adjacent pixels (crosstalk) have been discussed.
Japanese Patent Application Laid-Open No. 2003-258232 discusses a configuration where a P type well region, which functions as an element isolation barrier to prevent charges from mixing between adjacent pixels, is formed in a deep region consistent with an N type well region of a photoelectric conversion element.
However, even with the P type well region disclosed in Japanese Patent Application Laid-Open No. 2003-258232, it may be difficult to sufficiently suppress carrier leakage. In general, in the photoelectric conversion apparatus, a transistor for reading charges from a photoelectric conversion element is provided around the photoelectric conversion element. It is not necessary that the photoelectric conversion elements are arranged at regular intervals. Further, the widths of P type well separating the photoelectric conversion elements may be different. Accordingly, the inventors of the present invention have found out that an amount of signal charge leaking from a certain photoelectric conversion element to the adjacent photoelectric conversion elements may vary according to the width of such a P type well region. If the amount of carrier leakage to the adjacent photoelectric conversion elements varies, image quality is degraded and correction by signal processing becomes difficult. If intervals between the photoelectric conversion elements are made to be equalized and the widths of the P type well regions are also made to be equalized, a degree of freedom of planar layout of transistors for reading signal charges is decreased and reduction of pixels becomes difficult.
It is an object of the present invention to provide a photoelectric conversion apparatus capable of reducing variation in charges mixing into the adjacent photoelectric conversion elements (pixels).